This invention relates to a method and burner for burning fuel in a furnace. More particularly, it relates to a method and burner for burning fuel with controlled NOx formation.
Generally, NOx-formation-inhibiting burners (hereinafter called low-NOx burners) for use in metal heating furnaces are classified as the double combustion type, spent-gas recirculation type, steam injection type, and so on. The double combustion system performs primary combustion with a relatively small amount of air, then secondary combustion with abundant air. The spent-gas recirculation system dilutes the air and/or fuel with the spent gas introduced from the furnace to the burner tile port. The steam injection type dilutes the air and/or fuel with steam, instead of the spent gas, injected into the burner tile port.
All these conventional low-NOx burners are large, complex, costly, and difficult to maintain.
This invention is based on the spent-gas recirculation system. Conventional burners of this type, for example, have suffered from the following difficulties. Introduction of the spent gas to the burner tile port has necessitated a complex structure. More specifically, the spent gas in the furnace is drawn to the burner tile port through a lead-in port provided in the furnace wall. Or, the spent gas drawn from the furnace is forcibly supplied to the burner tile port with a fan. With such structures, the conventional low-NOx burners unavoidably become large, complex and difficult to maintain and inspect.
Modification of a conventional ordinary burner to the low-NOx type calls for much cost and long furnace shutdown. Therefore, there has been a large demand for a small, simple, low-maintenance-cost fuel burning method and burner with high NOx-controlling ability.